Multi-frequency acoustic vibration transmission method and system

ABSTRACT

A method and system ( 50 ) for inducing multi-frequency vibrations in a vibration propagating structure, for example a seat ( 52 ), is disclosed. The system is comprised of an acoustic vibration transducer unit ( 12 ) mounted on a relatively flat and rigid surface ( 54 ′) such that the direction of movement of an actuating element in the unit is parallel to the surface. When the unit is driven by an amplified low frequency audio signal a person sitting in the seat experiences vibrations. Additionally, a series of vibration propagating structures, for example a row of seats at a movie theatre, can be connected in series via vibration-propagating members ( 60 ) between adjacent seats thereby allowing a single acoustic vibration transducer unit to propagate vibrations to all connected seats.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application is a National Phase application ofInternational Application No. PCT/CA02/01412, filed 13 Sep. 2002, whichclaims priority from Canadian Application Nos. 2,357,304, filed 13 Sep.2001, 2,364,129, filed 5 Dec. 2001 and 2,382,310, filed 25 Apr. 2002.All of the above referenced applications are hereby incorporated hereinby reference.

TECHNICAL FIELD

[0002] The present invention relates to an apparatus and system for thetransmission of multi-frequency acoustic vibrations. In particular, thepresent invention relates to a method and system for the transmission oflow frequency audio signals recorded on a film, video or musicsoundtrack in the form of vibrations which can be sensed by aviewer/listener.

BACKGROUND ART

[0003] Given that deep base vibrations are generally found to besympathetic to the listener, in order to enhance the audio component ofan entertainment system a number of systems have been proposed whichconvert the bass audio signal to a vibration. These systems typicallyinclude a transducer, motor or other mechanical device which is capableof converting the audio input signal into a vibration. As a result,instead of or in addition to being heard, the bass signal is perceivedthrough tactile senses.

[0004] Additionally, imparting a vibration to the viewer of a movingimage which is synchronized with the moving image provides an additionaldimension which can be exploited in order to enhance the viewingexperience. Therefore, a variety of entertainment and simulation systemshave been proposed which combine projected images with synchronisedmovement and vibrations. The prior art reveals systems which use highintensity, low frequency noise synchronized to a projected movingpicture film or video to produce physiological sensations, for example ashaking sensation to simulate the effect of an earthquake, in theaudience. Earlier prior art systems conduct movement or vibrations to aseated, or in some cases standing, viewer or viewers by a variety ofmechanical means, including those based on the control of compressed airor hydraulics.

[0005] The introduction of multi-track digital audio combined withmoving picture film or high resolution video projectors has lead to anincrease in the common place combination of moving projected images withcomplex and high quality directional hi-fidelity audio sound tracks. Ina home entertainment system, for example, typically five (5) audiochannels are used to supply input to four (4) satellite speakerspositioned around the viewer and a single front speaker while a sixthaudio channel is used to supply a lower frequency subwoofer bassspeaker. In some cases a high intensity, low frequency sound supplied tothe bass speaker provides the viewer with the sensation of vibrations.In order to further amplify the vibrations a variety of acoustictransducers have been proposed which, when supplied with an appropriatelow frequency audio signal, generate high intensity vibrations which canbe perceived through tactile senses but not heard.

[0006] Known in the art are acoustic transducers where the movingelement is deflected in a direction generally perpendicular to a rigidsurface to which the transducer is attached. The prior art alsodiscloses acoustic transducers which are securely mounted to a hardrelatively flat surface, for example a floor, a chair back or underneaththe base of a chair. The transducers use the surface to which they aremounted as a means for transmitting vibrations to a person or persons incontact with the surface. These prior art acoustic transducers generatevibrations either percussively, for example by repeatedly rapping thecam of a solenoid against the hard flat surface, or by accelerating arelatively large mass back and forth relative to the surface. In boththese prior art assemblies the movement of the cam or the mass isperpendicular to the surface to which the acoustic transducer isattached.

[0007] One drawback of the above prior art acoustic transducers is thatthe transducer has a characteristically uneven frequency response with adominant resonant frequency being generally excited when the surface isstruck. This frequency is independent of the frequency or force withwhich the surface is hit. Still another drawback is that the vibrationspropagate in only a limited manner and therefore in large installationssuch as cinemas a large number of transducers are needed in order toconvey the vibrations to the entire audience. An additional drawback isthat in all installations in order to successfully induce vibrations theacoustic transducer(s) must be securely mounted to a rigid surface whichleads to difficulties in installation and removal, especially for homeapplications.

SUMMARY OF THE INVENTION

[0008] The present invention overcomes the above and other drawbacks byproviding a method of inducing multi-frequency acoustic vibrations in avibration-propagating structure. The method comprises positioning anelongate vibrating member generally parallel to and in physical contactwith the structure and producing in the elongate vibrating member themulti-frequency acoustic vibrations. The multi-frequency acousticvibrations propagate both through the elongate vibrating member and thestructure in physical contact with the elongate vibrating member andinduce in the structure the multi-frequency acoustic vibrations.

[0009] Also provided is a method of inducing multi-frequency acousticvibrations in a series of vibration-propagating structures. The methodcomprises positioning an elongate vibrating member in physical contactwith a first one of the structures and in a direction generally parallelto the series of structures. The direction constitutes a direction ofpropagation of the multi-frequency acoustic vibrations. Each pair ofmutually adjacent structures of the series are interconnected through anelongate vibration- propagating member generally parallel to thedirection of propagation. The multi-frequency acoustic vibrations areproduced in the elongate vibrating member which are propagated in thedirection of propagation from the elongate vibrating member, the firststructure, and the other structures of the series through the elongatewave-propagating members.

[0010] Additionally, a system for inducing multi-frequency acousticvibrations in a vibration-propagating structure is provided. The systemis comprised of an elongate vibrating member for being positionedgenerally parallel to and in physical contact with the structure and agenerator of the multi-frequency acoustic vibrations connected to theelongate vibrating member. In operation, the generator produces themulti-frequency acoustic vibrations in the elongate vibrating member.The multi-frequency acoustic vibrations are propagated both through theelongate vibrating member and the structure in physical contact with theelongate vibrating member to induce in the structure the multi-frequencyacoustic vibrations.

[0011] In a particular embodiment the generator is mounted within theelongate vibrating member to form an acoustic vibration transducer unit.

[0012] Furthermore, in a particular embodiment the vibration-propagatingstructure comprises a seating unit with cushions wherein the acousticvibration transducer unit is adapted to be positioned parallel to andtransversally of the seating unit between cushions of the seating unit.

[0013] Also, in a particular embodiment the vibration-propagatingstructure comprises a seating unit with a backrest having a rear faceand the acoustic vibration transducer unit is fastened horizontally andtransversally to the rear face of the backrest and extends generallyparallel to the rear face of the backrest.

[0014] There is also provided a system for inducing multi-frequencyacoustic vibrations in a series of vibration-propagating structures. Thesystem comprises an elongate vibrating member for being positioned inphysical contact with a first one of the structures and in a directiongenerally parallel to the series of structures, the directionconstituting a direction of propagation of the multi-frequency acousticvibrations. A generator of multi-frequency acoustic vibrations connectedto the elongate vibrating member. Additionally, an elongatevibration-propagating member for interconnecting each pair of mutuallyadjacent structures of the series is provided for. The elongatevibration-propagating member is generally parallel to the direction ofpropagation. In operation, the generator produces the multi-frequencyacoustic vibrations in the elongate vibrating member, and themulti-frequency acoustic vibrations propagate in the direction ofpropagation from the elongate vibrating member, the first structure, andthe other structures of the series through the elongate wave-propagatingmembers.

[0015] In a particular embodiment the elongate vibrating member iscylindrical.

[0016] In another particular embodiment the generator is mounted withinthe elongate vibrating member to form an acoustic vibration transducerunit.

[0017] In still another particular embodiment the elongatevibration-propagating members are tubular.

[0018] In another particular embodiment the vibration-propagatingstructures each comprise a seating unit with a backrest having a rearface and the elongate vibrating member is fastened to the rear face ofthe backrest of one of the seating units and extends generally parallelto the direction of propagation of the multi-frequency acousticvibrations.

[0019] In still another particular embodiment the series ofvibration-propagating structures comprises a row of seating units eachhaving a backrest with a rear face. The elongate vibration-propagatingmembers each interconnect the rear faces of the backrests of twoadjacent seating units corresponding to one pair of mutually adjacentvibration-propagating structures and extend generally parallel to thedirection of propagation of the multi-frequency acoustic vibrations.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The foregoing features of the invention will be more readilyunderstood by reference to the following detailed description, takenwith reference to the accompanying drawings, in which:

[0021]FIG. 1 is is a cross-sectional view of an acoustic vibrationtransducer in accordance with an illustrative embodiment of the presentinvention;

[0022]FIG. 2 is a cross-sectional view along 2-2 in FIG. 1 of anacoustic vibration transducer in accordance with an illustrativeembodiment of the present invention;

[0023]FIG. 3 is an elevated back view of a system for inducingmulti-frequency acoustic vibrations in a structure in accordance with aparticular illustrative embodiment of the present invention;

[0024]FIG. 4 is an elevated back view of a system for inducingmulti-frequency acoustic vibrations in a series of structures inaccordance with a particular illustrative embodiment of the presentinvention; and

[0025]FIG. 5 is an elevated front view of a system for inducingmulti-frequency acoustic vibrations in a structure in accordance with analternative illustrative embodiment of the present invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0026] An illustrative embodiment of the acoustic vibration transducerand vibration transmission system will now be described.

[0027] In general, the operation of the vibration transmission system asdescribed hereinbelow is as follows: A source of sound, such as apre-recorded audio track or the soundtrack of a film, is fed into anamplifier which converts the audio track or soundtrack into a varyingvoltage. According to principles well known in the art, either thesource of sound prior to amplification or the varying voltage is lowpass filtered to form a low frequency voltage signal. The low frequencyvoltage signal is input to an inductive coil held in a strong magneticfield. Current passing through the coil induces a magnetic flux whichcauses the coil to be deflected by the magnetic field. The extent anddirection of the deflection is related to both the direction andmagnitude of the current passing through the coil. An actuating elementon which the coil has been securely mounted is also deflected along withthe coil. The actuating element induces vibrations in a transducerhaving frequencies and magnitudes related to those present in the inputsignal.

[0028] Referring now to FIG. 1, the acoustic vibration transducer isgenerally referred using the reference numeral 10. The acousticvibration transducer 10 is comprised of a hollow elongate housing 12fabricated from a rugged dense material providing a solid, rigidenclosure. In an illustrative embodiment the housing 12 is fabricatedfrom a rolled laminated cardboard although it will be apparent to one ofordinary skill in the art that a variety of materials such ascomposites, fibreglass, PVC, plastic, metals such as aluminum or woodmay also be suitable materials in a particular implementation. Thehousing 12 is preferably of cylindrical/tubular form although otherelongate shapes, such as rectangular, will also be suitable.

[0029] An elongate actuating element 14 is suspended within and coaxialto the housing 12 towards a first end 16 by an annular suspensionmembrane 18 and annular rigid support 20 and towards the second end 22by an annular support membrane 24. Suspended in this manner, theactuating element 14 is restricted in movement along an axis coaxialwith the housing 12. In the illustrative embodiment the actuatingelement 14 is in the form of an elongate cylindrical tube which definesa hollow region 26. However, the cross section of the actuating elementcould be of another form, for example square or triangular.Additionally, the actuating element 14 could also be fabricated from asolid material or the hollow region 26 could be filled with material.

[0030] Additionally, in an illustrative embodiment the actuating element14 is fabricated from a section of aluminum tubing although it will beapparent to one of ordinary skill in the art that a variety of materialssuch as a rolled laminated cardboard, composites, fibreglass, PVC,plastic, metals other than aluminum or wood may also be suitablematerials in a particular implementation.

[0031] The suspension membrane 18 is fabricated from a pliant materialwhich, although flexible, is resistant to stretching. The suspensionmembrane 18 is securely attached along an inside edge 28 to theactuating element 14 and along an outside edge 30 to the annular rigidsupport 20. Additionally, the suspension membrane 18 should be such thatwhen no axial force is applied to the actuating element 14, theactuating element 14 returns to a predefined resting position. In anillustrative embodiment the suspension membrane 18 is fabricated fromleather although other suitable materials such as nylon or otherresilient cloths or materials may be used. The suspension membrane 18transmits forces generated by movements of the actuating element 14 tothe housing 12 via the rigid support 20.

[0032] The support membrane 24 is fabricated from a material which,although maintaining the second end 22 of the actuating element 14 incoaxial relation with the housing 12 and securely attached along aninside annular edge 32 to the actuating element 14, does not resistaxial movement of the actuating element 14. In an illustrativeembodiment the support membrane 24 is fabricated from a high qualitypaper which is folded into an accordion shape.

[0033] Referring to FIG. 2 in addition to FIG. 1, the means for excitingthe actuating element 14 to movement will now be described. The windingsof an inductive coil 34 are wound around or imbedded in the outersurface of the actuating element 14. An annular permanent magnet 36 issandwiched between an annular yoke plate 38 and back plate/t-yoke 40.Both the annular yoke plate 38 and the back plate/t-yoke 40 aretypically fabricated from low carbon steel. As is well known to those ofordinary skill in the art the combination of the annular permanentmagnet 36, yoke plate 38 and back plate/t-yoke 40 form a magneticcircuit and serve to concentrate the magnetic field (not shown) producedby the magnet 36 in the region of the inductive coil 34.

[0034] Application of an input signal across the inductive coil 34causes the actuating element 14 to be deflected with a direction andmagnitude proportional to the input signal in accordance with principleswhich are well known in the art. Application of a sinusoidal or complexsinusoidal input signal across the inductive coil 34 induces areciprocating movement in the actuating element 14 with a magnitude anddirection proportional to that of the input signal. This movement istransmitted by means of the suspension membrane 18/annular rigid support20 assembly to the housing 12.

[0035] Although the means for exciting the actuating element 14 has beenillustratively described in the form of a solenoid driven by a suitablyamplified input signal, it will be understood to one of ordinary skillin the art that other exciting means could be used. For example theactuating element 14 could be formed entirely or partially of a ferrousmetal and the inductive coil 34 wound around a portion of the housing12. Other means could also be used including, for example, compressedair, hydraulics, etc.

[0036] Referring back to FIG. 1, the first end 42 of the housing 12 isenclosed by a cover 44 in order to protect the actuating element 14 fromdamage. The second end 46 of the housing 12 is also enclosed in a cover48 although the backing plate/t-yoke assembly 40 can also in someconfigurations serve this purpose.

[0037] Depending on the type of installation, the diameter of thehousing 12 is sufficiently small, typically around ten (10) centimeters,in order that the acoustic vibration transducer 10 can be installedacross the back of a seat (not shown) without blocking, for example, thepassageway between rows of seats. Alternatively the acoustic vibrationtransducer 10 can be installed in the base of the seat. Additionally,the over all shape of the acoustic vibration transducer 10 is preferablyelongate and cylindrical which, amongst other advantages, simplifies itsattachment to a given surface. Note, however, that in a particularapplication the diameter of the acoustic vibration transducer 10 may beequal or slightly larger than its over all length (not shown).

[0038] The inductive coil 34 is typically driven with a complexsinusoidal audio signal between 1 and 200 Hertz output from anappropriate amplifier. A typical source of such a signal would be thesub-woofer output on a conventional surround sound audio amplifier.Tests with an accelerometer have shown that the response of the acousticvibration transducer unit 10 to an input sinusoid is very good withvirtually flat response over the entire 1-200 Hertz band.

[0039] Referring now to FIG. 3 an illustrative embodiment of a systemfor inducing system multi-frequency acoustic vibrations in a seat 50 isdisclosed. The seat 50 has a backrest 52 comprising a rear panel 54 madeof a rigid material, for example laminated wood or fibreglass.Illustratively, the acoustic vibration transducer unit 10 is securelymounted to the rear panel 54 of the seat 50 a pair of longitudinallyspaced apart U-shaped braces as in 56 each having two opposite endsscrewed into the rear panel 54.

[0040] Referring now back to FIG. 1 in addition to FIG. 3, the acousticvibration transducer unit 10 is mounted such that the axis of directionof movement of the actuating element 14 is substantially parallel to thesurface of the backrest 52. Although in this illustrative embodiment theacoustic vibration transducer unit 10 is mounted such that this axis isparallel to the ground, in a particular embodiment the acousticvibration transducer unit 10 could also be mounted such that this axisis not parallel to the ground.

[0041] Referring now to FIG. 4, another illustrative embodiment isconcerned with a system for inducing multi-frequency acoustic vibrationsin a row 58 of seats 50 of a movie theatre. In this illustrativeembodiment, each seat 50 has a backrest 52 comprising a rear panel 54made of rigid material such as laminated wood or fibreglass. The row ofseats 50 then forms a series of vibration-propagating structures.

[0042] In the illustrative embodiment of FIG. 4, the acoustic vibrationtransducer unit 10 is fastened to the rear of the backrest 52 through apair of longitudinally spaced apart U-shaped braces as in 56 each havingtwo opposite ends screwed into the rear panel 54. Also, the rear panels54 of each pair of mutually adjacent seats 50 are mechanicallyinterconnected through a section of metallic tube 60. Each section ofmetallic tube 60 has two opposite ends respectively screwed into therear panels 54 of the corresponding pair of mutually adjacent seats 50.

[0043] To efficiently transfer the multi-frequency acoustic vibrationsfrom the acoustic vibration transducer unit 10 to the rear panel 54′ ofthe seat 50′, the housing 12 of the acoustic vibration transducer unit10 is mounted generally parallel to this rear panel 54′ and in physicalcontact therewith. The multi-frequency acoustic vibrations thenpropagate through the rear panel 54′ and then through the entirestructure of the seat 50′. Of course, a person sitting in the seat 50′will experience these vibrations with an intensity depending on theamplitude of the multi-frequency acoustic vibrations.

[0044] In operation, the multi-frequency acoustic vibrations generatedin the housing 12 are transferred to and propagate through the rearpanel 54′ of the seat 50′. Then the multi-frequency acoustic vibrationswill propagate from rear panel 54 to rear panel 54 through the sectionsof metallic tubes 60 in two opposite directions parallel to the row ofseats 50. In order to ensure efficient propagation of themulti-frequency acoustic waves:

[0045] the acoustic vibration transducer unit 10 is disposedsubstantially horizontal to the ground and substantially parallel to therow of wooden rear panels 54; and

[0046] the metallic tubes 60 are also disposed horizontal to the groundand substantially parallel to the row of wooden rear panels 54,therefore substantially parallel to the housing 12 of the acousticvibration transducer unit 10.

[0047] The multi-frequency acoustic vibrations propagated through eachrear panel 54 are thus transferred through the entire structure of thecorresponding seats 50. Persons sitting in the seats 50 will experiencethese vibrations with an intensity depending on the amplitude of themulti-frequency acoustic vibrations. Tests with an accelerometer haveshown that the amplitude of the vibrations and therefore the sensationof vibration experienced by a person sitting in one of the seats 50 iscomparable for all seats 50. However, tests have also revealed that thenumber of seats 50 which can be driven by a single acoustic vibrationtransducer unit 10 without seriously degrading performance will dependon a number of factors including:

[0048] the materials used to fabricate the rear panels 54;

[0049] the co-alignment of the rear panels 54;

[0050] the co-alignment of the series of metallic tubes 60; and

[0051] the alignment of the series of metallic tubes 60 with the housing12 of the acoustic vibration transducer unit 10.

[0052] Therefore, efficient propagation of the multi-frequency acousticvibrations through the row of seats 50 is obtained when the acousticvibration transducer unit 10 and the metallic tubes 60 are oriented inthe direction of propagation of these multi-frequency acousticvibrations. More specifically, the acoustic vibration transducer unit 10and the metallic tubes 60 are substantially horizontal and substantiallyparallel to the row of seats 50.

[0053] Referring now to FIG. 5, an alternative illustrative embodimentis concerned with a system for inducing multi-frequency acousticvibrations in a seating unit 62 comprised of seat cushions as in 64resting on a stable support 66, a rigid back rest 68 and a comfortableupholstered covering 70 on the backrest 68. In this illustrativeembodiment the diameter of the housing 12 of the acoustic vibrationtransducer unit 10 is preferably small enough to be placed behind andunderneath the cushions 64. In order to ensure efficient propagation ofacoustic vibrations, the acoustic vibration transducer unit 10 ispositioned parallel to the stable support 66 and back rest 68 andtransverse to the direction of seating on the seating unit 62.

[0054] Still referring to FIG. 5, a suitable diameter of the housing 12is about five (5) centimeters. The acoustic vibration transducer unit 10is preferably centred on the seating unit 62 and the housing 12 ofsufficient length that it spans a large portion of the length of theseating unit 62. Additionally, tests have shown that the acousticvibration transducer unit 10 functions well in this embodiment withoutsecurely fastening the housing 12 to the seating unit 62, therebygreatly simplifying the installation and removal of the acousticvibration transducer unit 10.

[0055] Although the present invention has been described using by way ofexample the transmission of vibrations derived from an audio signal, thepresent invention has many other potential uses. For example, anadjustable or programmable complex signal generator could be used asinput to the acoustic vibration transducer unit 10 and the systemapplied for therapeutic purposes. Additionally, the system could alsoserve as a component in a vibration reduction system. For example, theengine of a motor vehicle or aircraft typically generate vibrationswhich are perceived by the passengers and often found unpleasant. Bysupplying the acoustic vibration transducer unit 10 with a signalgenerated to take advantage of phase cancellation techniques theperception of unpleasant vibrations can either be reduced or completelysuppressed.

[0056] Although the present invention has been described hereinabove byway of an illustrative preferred embodiment thereof, this embodiment canbe modified at will, within the scope of the present invention, withoutdeparting from the spirit and nature of the subject of the presentinvention.

[0057] The embodiments of the invention in which an exclusive propertyor privilege is claimed are defined as follows:

What is claimed is:
 1. A method of inducing multi-frequency acousticvibrations in a vibration-propagating structure, comprising: positioningan elongate vibrating member generally parallel to and in physicalcontact with the structure; and producing in said elongate vibratingmember the multi-frequency acoustic vibrations, the multi-frequencyacoustic vibrations propagating both through said elongate vibratingmember and the structure in physical contact with said elongatevibrating member to induce in the structure the multi-frequency acousticvibrations.
 2. A method of inducing multi-frequency acoustic vibrationsin a series of vibration-propagating structures, comprising: positioningan elongate vibrating member in physical contact with a first one of thestructures and in a direction generally parallel to the series ofstructures, said direction constituting a direction of propagation ofthe multi-frequency acoustic vibrations; interconnecting each pair ofmutually adjacent structures of the series through an elongatevibration-propagating member generally parallel to said direction ofpropagation; producing in said elongate vibrating member themulti-frequency acoustic vibrations; and propagating the multi-frequencyacoustic vibrations in said direction of propagation from said elongatevibrating member, the first structure, and the other structures of theseries through said elongate wave-propagating members.
 3. A system forinducing multi-frequency acoustic vibrations in a vibration-propagatingstructure, comprising: an elongate vibrating member for being positionedgenerally parallel to and in physical contact with the structure; and agenerator of the multi-frequency acoustic vibrations connected to saidelongate vibrating member; wherein, in operation, said generatorproduces the multi-frequency acoustic vibrations in said elongatevibrating member, and the multi-frequency acoustic vibrations propagateboth through said elongate vibrating member and the structure inphysical contact with said elongate vibrating member to induce in saidstructure the multi-frequency acoustic vibrations.
 4. A vibrationinducing system as defined in claim 3, wherein said generator is mountedwithin said elongate vibrating member to form an elongate acousticvibration transducer unit.
 5. A vibration inducing system as defined inclaim 4, wherein: the vibration-propagating structure comprises aseating unit with cushions; and said elongate acoustic vibrationtransducer unit is adapted to be positioned parallel to andtransversally of said seating unit between said cushions of said seatingunit.
 6. A vibration inducing system as defined in claim 4, wherein: thevibration-propagating structure comprises a seating unit with a backresthaving a rear face; and said elongate acoustic vibration transducer unitis fastened horizontally and transversally to said rear face of saidbackrest, said elongate vibrating member extending generally parallel tosaid rear face of said backrest.
 7. A system for inducingmulti-frequency acoustic vibrations in a series of vibration-propagatingstructures, comprising: an elongate vibrating member for beingpositioned in physical contact with a first one of the structures and ina direction generally parallel to the series of structures, saiddirection constituting a direction of propagation of the multi-frequencyacoustic vibrations; a generator of said multi-frequency acousticvibrations connected to said elongate vibrating member; an elongatevibration-propagating member for interconnecting each pair of mutuallyadjacent structures of the series, said elongate vibration-propagatingmember being generally parallel to said direction of propagation;wherein, in operation, said generator produces the multi-frequencyacoustic vibrations in said elongate vibrating member, and the multifrequency acoustic vibrations propagate in said direction of propagationfrom said elongate vibrating member, the first structure, and the otherstructures of the series through the elongate wave-propagating members.8. A vibration inducing system as defined in claim 7, wherein said theelongate vibrating member is cylindrical.
 9. A vibration inducing systemas defined in claim 7, wherein said generator is mounted within saidelongate vibrating member to form an acoustic vibration transducer unit.10. A vibration inducing system as defined in claim 7, wherein saidelongate vibration-propagating members are tubular.
 11. A vibrationinducing system as defined in claim 7, wherein: thevibration-propagating structures each comprise a seating unit with abackrest having a rear face; and said elongate vibrating member isfastened to said rear face of said backrest of one of said seating unitscorresponding to said , one structure, said elongate vibrating memberextending generally parallel to said direction of propagation of themulti frequency acoustic vibrations.
 12. A vibration inducing system asdefined in claim 7, wherein: the series of vibration-propagatingstructures comprises a row of seating units each having a backrest witha rear face; and said elongate vibration-propagating members eachinterconnect said rear faces of said backrests of two adjacent seatingunits corresponding to one pair of mutually adjacent vibrationpropagating structures, said elongate vibration-propagating membersextending generally parallel to said direction of propagation of themulti-frequency acoustic vibrations.